Process for making a mold piece having a main curved surface bearing a utilitary microstructure

ABSTRACT

A process for making a mould piece having a main curved surface bearing an utilitary microstructure which comprises transferring a utilitary microstructure from a master piece main surface to a main surface of a flat cured elastomeric film; pressing the cured elastomeric film and a master article against each other so as to conform the overall shape of said cured elastomeric film to the curved shape of the main surface of the master article and to spread over a curable coating composition between the curved main surface of the master article and the main surface bearing the replica of the said utilitary microstructure of the cured elastomeric film; curing the coating composition; removing the cured elastomeric film and depositing a layer of a metal or a metallic alloy on the exposed main surface of the hard coating of the master article; and recovering said metal or metallic alloy layer to obtain a mould piece having a curved main surface bearing a replica of said transferred utilitary microstructure.

The present invention relates to the field of microstructure replicationand more precisely to a process for making a piece having a main curvedsurface bearing an utilitary microstructure. In particular, the presentinvention concerns a process for making such a piece usable for massproduction of moulded articles, in particular ophthalmic lenses, havinga main surface bearing an utilitary microstructure and preferably amicrostructure having anti-reflection properties.

It is known to impart utilitary microstructures such as holograms,diffraction gratings and microstructures having antireflectionproperties in different kinds of articles.

One particular technique for manufacturing these articles consists inmoulding the articles in moulds in which at least one surface of themoulding cavity bears a microstructure.

Many different methods for obtaining mould pieces and especially lensmould pieces having a main surface of the moulding cavity bearing anutilitary microstructure are described in international patentapplication WO 99/29494.

In document WO 99/29494, the utilitary microstructure is initiallyobtained by an interferential method. Such a method is well known forthe replication of microstructure in an article having flat surfaces.However, if this method is used for creating microstructure directly ina non planar surface, some distortions of the pattern of interferencefringes creating the microstructure may occur. It is then necessary tocreate a pattern of interference fringes that is itself modified to takeinto account the curvature of the surface on which the microstructuremust be imprinted.

When the article on which the microstructure is to be transferred is anophthalmic lens or a lens mould, whose article surfaces are designedaccording to each spectacle lens wearer, it is a complicated andcumbersome procedure adapting the pattern of interference fringes to thecurvature of each lens.

One solution provided in document WO 99/29494 is to imprint themicrostructure in a first surface of a flexible flat support, applyingthe opposite surface of this support onto the main surface of a mouldpiece by modifying the shape of the flexible flat support, so as toconform its geometry to the geometry of the mould piece main surface inorder to obtain a composite mould having a curved moulding main surfacebearing the microstructure.

One problem with that solution is that it is difficult to find supportmaterials that can be at the same time:

sufficiently soft and flexible to withstand shape deformation withoutinducing cracking at the support surface;

sufficiently stable to keep the dimensional integrity of themicrostructure during the subsequent lens moulding process, inparticular when high temperatures are required as for example during thecuring step of the lens composition;

sufficiently compatible with different monomer compositions, i.e. beingchemically inert and providing sufficient wettability with the monomercompositions to adequately fill the microstructures, and

sufficiently durable to withstand the moulding of a high number ofarticles such as ophthalmic lenses (mass production).

European patent EP 400.672 describes a technique for forming an unitarymould having a microstructure integrally formed on its inside surface.More particularly, a film having one surface bearing a hologram, adiffraction grating or other microstructure is firmly attached throughits surface opposite to the surface bearing the microstructure onto thesurface of a model of the article to be moulded. Then, a mould piececonforming to the outside shape of at least a portion of the model isformed by electrodeposition of metal onto the surface of the filmattached to the model.

The deposited metal is then separated from the model and mechanicallyreinforced for use as a mould piece, for example in standard injectionmoulding.

This technique necessitates that the flexible film bearing themicrostructure be firmly attached to the surface of a model of articlesto be moulded. Such an attachment step increases the risk of adeterioration of the film bearing the microstructure such as for examplea cracking of the film, in particular when the surface model is a curvedsurface.

The publication “Soft lithography” Younan Xia, George M. Whitesides;Angew. Chem, Int. Ed. 1998, 37, 550-575, describes on page 764 a methodof replica moulding against a deformed polydimethylsiloxane mould.According to this method, a microstructure is first imprinted in apolydimethylsiloxane mould. The relief features on thepolydimethylsiloxane mould are reconfigured by mechanical deformationand the deformed structure is replicated by casting a UV curable liquidpolyurethane or a thermally curable epoxy against thepolydimethylsiloxane mould.

More particularly, in one embodiment, a thin polydimethylsiloxane (PDMS)mould (about 50 micrometers thick) having a surface bearing amicrostructure is bent so that the microstructure bearing surface of thePDMS mould is brought into conformal contact with curved surface (lens)coated with a thin film of liquid polyurethane.

After curing of the polyurethane, the PDMS mould is removed to revealthe polyurethane replica on the surface of the cylindrical substrate.Finally, one thus obtains a final lens coated with a polyurethanecoating having a microstructure imprinted in it.

Such a method is not usable in practice for mass production.

Thus, the object of the present invention is to provide a simple,reproducible and quick process for making a curved mould piece bearing autilitary microstructure, said curved mould piece being usable inpractice for mass production of articles such as lenses bearing on amain surface thereof an ufilitary microstructure.

According to the invention, there is provided a process for making amould piece having a main curved surface bearing an utilitarymicrostructure which comprises:

a) providing a master piece having a flat main surface bearing autilitary microstructure;

b) transferring said utilitary microstructure from the master piece mainsurface to a main surface of a flat cured elastomeric film;

c) recovering the flat cured elastomeric film having a main surfacebearing a replica of said utilitary microstructure;

d) providing a master article having a main curved surface;

e) applying a curable coating composition:

-   -   on the main curved surface of the master article, or    -   on the main surface bearing the replica of said utilitary        microstructure of the flat cured elastomeric film, or    -   on both surfaces.

f) placing the main surface bearing the replica of said utilitarymicrostructure of the flat cured elastomeric film and the main coatedsurface of the master article in front of each other;

g) pressing said cured elastomeric film and said master article againsteach other so as to conform the overall shape of said cured elastomericfilm to the curved shape of the main surface of the master article andto spread over the curable coating composition between the curved mainsurface of the master article and the main surface bearing the replicaof said utilitary microstructure of the cured elastomeric film;

h) curing the coating composition;

i) removing the cured elastomeric film and recovering a hard coatedarticle having a main curved surface coated with a hard coating havingan exposed main surface bearing a transferred utilitary microstructure;

j) depositing a layer of a metal or a metallic alloy on said exposedmain surface of the hard coating of the article, and

k) recovering said metal or metallic alloy layer to obtain a mould piecehaving a curved main surface bearing a replica of said transferredutilitary microstructure.

The invention will now be described in connection with the drawings inwhich:

FIGS. 1A to 1J illustrate the main steps of the process according to theinvention;

FIG. 2 is a perspective view of a jig specifically designed for pressingthe cured elastomeric film and the master article (step g), the jigbeing in its open position prior to pressing;

FIG. 3 is a perspective view of the jig of FIG. 2 in its closedposition, i.e. at the end of the pressing step (step g); and

FIG. 4 is a schematic view of a jig for holding the lens during theelectrodeposition process.

As shown in FIG. 1A, there is first provided a flat master mould 1having a main flat surface bearing a utilitary microstructure 2.

The flat master can be made of any suitable material but it ispreferably made of metal or a metallic alloy and in particular ofnickel.

The utilitary microstructure 2 may be any utilitary microstructure suchas a hologram, a diffraction grating, or a microstructure havingantireflection properties. Preferably, the utilitary microstructure is amicrostructure having antireflection properties.

The utilitary microstructure 2 which is borne by the main flat surfaceof the master piece 1 can be previously obtained by any availabletechnique including the one described in European patent application EP757.262 which concerns a process for obtaining a microgranular surfacecomprised of SiO₂.

A preferred method for obtaining the utilitary microstructure 2 is theinterferential method described in international patent application WO99/29494.

More precisely, the interferential process consists in making a patternof interference fringes by superimposing two coherent light waves, forexample two laser beams, and irradiating a photosensitive material layercoated onto a substrate through such pattern of interference fringes.

Then, by developing conventionally the photosensitive material layer, aperiodic microstructure is obtained.

Two irradiation steps for the photosensitive layer can be provided ifdesired by rotating the substrate, preferably by 90° after the firstirradiation step, and then the photosensitive material layer isdeveloped conventionally.

A periodic microstructure is then obtained in the plane. Thus, anisotropic structure may be obtained the antiglare properties of whichare independent from the sight angle.

Naturally, patterns of interference fringes having different oridentical pitches (i) and amplitudes (2A) can be formed. Also, saidirradiation steps may be repeated various times so as to obtain afterdevelopment a final microstructure formed with multiple superimposedmicrostructures.

Generally, the wavelength of the coherent light beams, for example laserbeams, is comprised between 170 and 510 nm and the pitch of the patternof interference fringes (and consequently of the periodic microstructurebeing obtained) is comprised between 100 and 300 nm. The amplitude 2A iscomprised generally between 100 and 300 nm.

Preferably plane light waves are used and so a sinusoidal microstructureis obtained.

The periodic microstructure may be generally defined in an orthogonalreference system (x, y, z) with the following equation (1):$\begin{matrix}{z = {{f\left( {x,y} \right)} = {{\sum\limits_{n = 1}^{k}\left\lbrack {{A_{n}{\sin\left( {2\quad\Pi\quad n\frac{x}{i}} \right)}} + {B_{n}{\cos\left( {2\quad\Pi\quad n\frac{x}{i}} \right)}}} \right\rbrack} + {\sum\limits_{m = 1}^{k}\left\lbrack {{C_{m}{\sin\left( {2\quad\Pi\quad m\frac{y}{i}} \right)}} + {D_{m}{\cos\left( {2\quad\Pi\quad m\frac{y}{i}} \right)}}} \right\rbrack}}}} & (1)\end{matrix}$

where A_(n), B_(n) are Fourier coefficients in the microstructure in thedirection x,

C_(m), D_(m) are Fourier coefficients in the microstructure in thedirection y, and

i is the pitch (period) of the microstructure.

Preferably, B_(n)=D_(m)=0, A_(n)=C_(m)=A (sinusoidal structure) and thepattern of interference fringes and, consequently, the microstructuremay be represented by the equation (2): $\begin{matrix}{z = {{f\left( {x,y} \right)} = {A\left\lbrack {{\sin\left( {2\quad\Pi\frac{x}{i}} \right)} + {\sin\left( {2\Pi\frac{y}{i}} \right)}} \right\rbrack}}} & (2)\end{matrix}$

where i is the period and A the half-amplitude.

Preferably, the utilitary microstructure is a periodically repetitivestructure having a period of 250 nm.

The flat master piece 1 is then placed in a container 3, for example ametallic container, with the microstructure 2 facing outwardly towardsthe open end of the container 3 (FIG. 1B).

As shown in FIG. 1C, an appropriate amount of an elastomeric filmforming curable composition 4 is then poured over the master piece 1.Although, UV and/or thermally curable compositions can be used, it ispreferred to use thermally curable compositions and in particularthermally curable polydimethylsiloxane (PDMS) compositions.

After curing the curable composition 4, a flat cured elastomeric film 5having a main surface 6 bearing a replica of the utilitarymicrostructure 2 is recovered as shown in FIG. 1D.

As previously indicated, the preferred flat cured elastomeric films arepreferably made of cured PDMS, such as those obtained by curing acurable PDMS composition Sylgard Elastomer 184.

Another suitable material for the elastomeric film is RTV 615™commercialised by G.E. silicones absorbing UV light under 214 nm.

Typically, the film 5 would have a thickness ranging from 1 to 2 mm.

Reproduction of such a silicone flat film 5 having a main surface 6bearing a utilitary microstructure starting from a nickel master pieceis disclosed in the article “Replication and compression of Bulk SurfaceStructures with Polydimethylsiloxane Elastomer”, D. J. Campbell, K. J.Beckman, C. E. Calderon, P. W. Doolan, R. H. Moore, A. B. Ellis, G. C.Lisensky, J. Chem. Educ. Vol. 76, 537 (1999).

Once recovered, the flat elastomeric film 5 is placed in a mountingframe 7 which holds the film 5 at its periphery (FIG. 1E).

As shown in FIG. 1F, there is then provided a master article 8 such asan ophthalmic lens having at least one main curved surface 9.Preferably, master article 8 is an ophthalmic lens in particular anophthalmic lens whose main curved surface is a spherical surface or apresbyopia correcting surface (i.e a progressive addition lens).

The master article 8 may be made of any material suitable for makingophthalmic lenses, but is preferably made of a plastic material, and inparticular of diethyleneglycol bis-allylcarbonate copolymère (CR39® fromPPG Industries) or polycarbonate (PC).

Other suitable materials for the master article 8 are glasses obtainedby polymerization of allyl monomers derived from bisphenol A, such asthose described in U.S. Pat. No. 4,959,429, polyalkyl(meth)acrylate inparticular polymethyl(meth)acrylate, polystyrene resins and resins basedon diallyl phtalate.

The preferred materials for the master article 8 are diethyleneglycolbis(allylcarbonate) polymers and copolymers and polycarbonate.

An appropriate amount of a curable composition 10 is then deposited onthe main curved surface 9 of the master article 8. Alternatively, thecurable composition 10 can be deposited on the main surface 6 bearingthe replica of the utilitary microstructure 2 of the flat elastomericfilm 5 or adequate amounts of the curable composition 10 may bedeposited on both the main surface 6 of the flat film and the curvedmain surface 9 of the master article 8.

Preferably, the curable composition is a UV curable composition.

Any well known method can be used for depositing the curablecomposition, such as dip coating and spin coating.

If necessary, it is possible to apply the curable composition in two ormore successive steps. For example, a first amount of curablecomposition is applied by dip or spin coating on either the surface 6 or9 and then a larger amount is applied on the centre surfaces 6 and/or 9.

Thickness of the deposited curable composition 10 will typically rangefrom 1 to 15 micrometers, preferably from 2 to 10 micrometers.

The curable coating composition 10 may be any curable coatingcomposition used in the ophthalmic lens technology.

The curable coating composition can comprise urethanes, siloxanes oracrylic materials.

A preferred class of coating composition is coating compositioncomprising (meth)acrylic monomers or oligomers. The preferred monomersare di(meth)acrylate or tri(meth)acrylate monomers, in particularpolyalkylene glycols di(meth)acrylates and/orpoly(alkylenoxy)di(meth)acrylates. Particularly preferred compositionsare those made of a mixture of butane diol diacrylate andpentaerythritoltriacrylate.

Other compositions that can be used, are for example those comprisinghydrolysates of alkoxysilanes, in particular of organopolyalkoxysilanes,such as methyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, andmethacryloxypropyltrimethoxy silane. Examples of such compositions aredisclosed in U.S. Pat. No. 4,211,823, WO 94/10230 and U.S. Pat. No.5,015,523.

The main surface 6 bearing the replica of the utilitary microstructure 2of the flat cured elastomeric film 5 and the main curved surface 9 ofthe master article 8 covered with the curable composition 10 are thenplaced in front of each other.

The cured elastomeric film 5 and the master article 8 are thereafterpressed against each other so as to conform the overall shape of thecured elastomeric film 5 to the curved shape of the main surface 9 ofthe master article 8 and to spread over the curable coating composition10 between the curved main surface 9 of the master article 8 and themain surface 6 bearing the replica of said utilitary microstructure 2 ofthe cured elastomeric film 5.

Pressing can be done by either stretching the film across the curvedmain surface 9 of the master article 8 or by directly applying apressure onto the surface of the flat elastomeric film 5 opposite to themain surface 6 bearing the replica of the utilitary microstructure 2 topress the flat elastomeric film 5 against the main curved surface 9bearing the curable composition 9 of the master article 8. The curablecomposition 10 is then cured, preferably cured by photoactinicradiation, preferably UV radiation when the composition 10 is aphotocurable composition.

Preferably, irradiation is made through the cured elastomeric film inorder to reach the photocurable composition.

After disassembling and removing of the cured elastomeric film 5 thereis recovered a hard coated master article 8 having its main curvedsurface 9 coated with a hard coating 10 having an exposed main surface11 bearing a transferred utilitary microstructure as shown in FIG. 1H.

As shown in FIG. 1A, a metal or metallic alloy layer usually, nickel, iselectrodeposited onto the exposed main surface 11 of the hard coat 10 ofthe master article 8.

Such an electrodeposition process is classical and is disclosed forexample in European patent application 400.672.

After disassembling there is recovered a metal or metallic alloy mouldpiece 13, having a curved main surface 14 bearing a replica of thetransferred utilitary microstructure which can be used for massproduction of moulded articles bearing a utilitary microstructure, suchas ophthalmic lenses.

Thickness of the metallic mould piece 13 typically will range from 0.3mm to 5 mm.

Although the mould piece 13 may be attached to a reinforcing element, itis preferably of such a thickness so that it can be used directlywithout requiring any reinforcing element. In that case, a metallicmould piece has generally at least 1 mm thickness.

There is represented in FIGS. 2 and 3 a specifically designed device orjig 20 for pressing a flat cured elastomeric film 5 bearing a replica ofthe utilitary microstructure.

Referring to FIG. 2, which is a perspective view of jig 20 in its openposition, i.e. before implementing of the pressing step (step g) of theinventive process, jig 20 comprises a base plate 21 and a tiltable filmholder 22 rotatably linked to the base plate 21. Base plate 21 comprisesa support 23 for the master article 8, generally at its centre. Support23 is preferably such that, when master article 8 is placed on support23, only the main curved surface of master article 8 coated with thecurable coating composition protrudes from support 23.

The film holder 22 comprises two separate complementary frames 24, 25defining a central opening, which can be clamped together by appropriatemeans such as screws 26, so that the flat cured film 5 is placed betweenframes 24, 25 and firmly maintained flat in sandwich between the twoseparate complementary frames 24, 25 after assembling.

As previously indicated, film holder 22 is rotatably linked to baseplate 21. For that purpose, complementary frames 24, 25 are rotatablylinked to an axle 27 through connecting means 28, 29. As shown in FIG.2, each connecting means 28, 29 comprise two separate parts that can befixedly clamped to complementary frames 24, 25 through fixing means suchas screws or bolts, thus allowing easy assembling and disassembling ofthe complementary frames 24, 25 and replacement of the film 5.

Each mounting means 28, 29 when assembled are rotatably linked with axle27.

The ends of axle 27 are fixedly mounted within two upright posts 31, 32protruding from the base plate 21 and spaced along one side thereof, andpreferably at two contiguous corners thereof.

Preferably, at least one stop, such as posts 33, 34, is provided nearthe base plate side opposite to axle 27 in order to adequately limitrotation of the film holder 22 towards base plate 21.

As shown in FIG. 2, master piece support 23 comprises two separateparts. A first part 23 a which is fixedly linked to or integrally madewith base plate 21 and a second removable part 23 b for accommodatingthe master piece 8.

The jig 20 operates as follows:

Film holder 22 is disassembled and the elastomeric film 5 is placedbetween the complementary frames 24, 25. Film holder 22 is reassembledand mounted on axle 27 with the microstructure bearing face of film 5facing base plate 21. A coated master piece 8 is placed on support 23with its coated curved face directed towards the film holder 22.

Then the film holder is rotated downwardly until it contacts stops 33,34.

The film contacts first the master piece 8 at its centre and then thecontact line moves outwards as the film holder 22 is lowered up tocontacting steps 33, 34. Thereafter coating is cured.

After curing, the film holder 22 is lifted back to recover a masterpiece with a microstructure imprinted in its coated surface for furthertreatments.

In FIG. 4, there is schematically shown a jig 30 for holding the masterpiece and particularly suitable for implementing the metal depositionstep (step j) and in particular an electrodeposition step.

As shown in FIG. 4, jig 30 comprises a thick, flat, plastic plate 31 inwhich a recess 32 has been machined.

Recess 32 is machined so that master piece 8 having a curved surfacebearing the microstructure is snuggly fitted in the recess 32 and onlythe microstructure bearing curved surface of the master piece 8protrudes from recess 32.

Before the electrodeposition step, the plate is coated with a thin layerof a photoresist 33 to promote adhesion between the nickel and theplastic and an initial very thin metal layer 34 is formed on the masterpiece and the plate by sputtering or evaporation. The contact linebetween the master piece 8 and the plate 31 is then painted with aconductive adhesive 35 to improve the electrical contact.

EXAMPLE

A mould piece having a curved surface bearing an utilitarymicrostructure is made using the overall process described above.

1. Copying of the Microstructure

The flat master piece was a nickel flat master piece of 125×125 mm sizeand 1 mm thick comprising a surface relief grating with a period of 250nm. This microstructure was initially obtained by holographic exposureof a photoresist.

The flat nickel master piece was then placed, with its imprintedmicrostructure facing up in a 150×150×30 mm metal container.

Then, a batch of a curable polydimethylsiloxane composition (Dow CorningSylgard Elastomer 184 from Dow Corning) was prepared with a ratio ofcuring agent to base of 1:15. After mixing the components thoroughly,the mixture was set aside for 15 minutes to allow bubbles to rise out ofthe composition. Next, the composition was poured into the metalcontainer to cover the master piece and set aside for 15 minutes toallow bubbles to rise out from the composition. Finally, the assemblywas put in an oven at 130° C. for 20 minutes to cure the composition.After cooling down to room temperature, the cured composition wascarefully removed from the nickel flat master piece in order to recovera cured elastomeric polydimethylsiloxane film having main surfacebearing a replica of the microstructure. The cured PDMS film is totallytransparent. The film has a thickness of several mm at this edge,whereas the portion thereof bearing the utilitary microstructure is 1-2mm thick.

2. Transfer of Microstructure to Master Lens Hard Coat

0.5 ml of a commercially available UV curable composition (SHC-3100Universal Coating from Gerber Coburn/LTI) are deposited on the convexsurface of a CR39® lens having a negative power of −2.00 dioptries.

The silicone film was mounted in the film holder of the jig described inconnection with FIGS. 2 and 3, with microstructure facing down, and filmholder was lowered over the lens and clamped in position.

The silicone film contacted the centre of the lens first and then thecontact line moved outwards as the sheet was lowered.

This excluded air bubbles from the interface. The height of the lens waschosen to ensure that the silicone film conformed exactly to the lenssurface.

The UV curable composition was then cured by irradiation during 3minutes with a UV light 130 mW/cm² intensity.

After separating the PDMS film from the lens, there was obtained a lenshaving a cured hard coat whose exposed surface bears a replica of themicrostructure.

3. Obtention of a Nickel Mould Piece by Electroforming.

The master lens is mounted in a jig as disclosed in connection with FIG.4. After deposition of a thin layer of a photoresist, an initial verythin layer of nickel is deposited by physical vapor deposition onto theexposed surface of the cured hard coat.

The contact line between the lens and the plastic plate is then paintedwith a conductive adhesive to improve the electrical contact.

The plastic plate is then mounted in a steel ring and the assemblyplaced in a classical electrodeposition device. The nickel coating wasincreased to 300 microns thickness by electrodeposition.

Thereafter, the master lens is withdrawn from the device and the nickellayer is separated from the master lens to recover a nickel mould piecehaving a main curved surface bearing a replica of the microstructure.

1-15. (canceled)
 16. A process for making a mold piece having a maincurved surface bearing a microstructure comprising: (a) providing amaster piece having a flat main surface bearing a microstructure; (b)transferring said microstructure from the master piece main surface to amain surface of a flat cured elastomeric film; (c) recovering the flatcured elastomeric film having a main surface bearing a replica of saidmicrostructure; (d) providing a master article having a main curvedsurface to be replicated; (e) applying a curable coating compositioneither: on the main curved surface of the master article, or on the mainsurface bearing the replica of said microstructure of the flat curedelastomeric film, or on both main surfaces; (f) placing the main surfacebearing the replica of said microstructure of the flat cured elastomericfilm and the main curved surface of the master article in front of eachother; (g) pressing said cured elastomeric film and said master articleagainst each other so as to conform the overall shape of said curedelastomeric film to the curved shape of the main surface of the masterarticle and to spread over the curable coating composition between thecurved main surface of the master article and the main surface bearingthe replica of the said microstructure of the cured elastomeric film;(h) curing the coating composition; (i) removing the cured elastomericfilm and recovering a hard coated article having a main curved surfacecoated with a hard coating having an exposed main surface bearing atransferred microstructure; (j) depositing a layer of a metal or ametallic alloy on said exposed main surface of the hard coating of themaster article; and (k) recovering said metal or metallic alloy layer toobtain a mold piece having a curved main surface bearing a replica ofsaid transferred microstructure.
 17. The process of claim 16, whereinthe master piece comprises a metal or metallic alloy piece.
 18. Theprocess of claim 17, wherein the metal is nickel.
 19. The process ofclaim 16, wherein transfer step (b) is performed by pouring a liquidcurable elastomeric composition over the main flat surface bearing themicrostructure of the master piece and curing the composition.
 20. Theprocess of claim 19, wherein the elastomeric composition is cured byheat curing.
 21. The process of claim 16, wherein the flat curedelastomeric film comprises a polysiloxane.
 22. The process of claim 21,wherein the polysiloxane is a polydimethylsiloxane.
 23. The process ofclaim 16, wherein the flat cured elastomeric film has a thicknessranging from 1 to 2 mm.
 24. The process of claim 16, wherein the flatcured elastomeric film is held by a peripheral frame during pressingstep (g).
 25. The process of claim 16, wherein the curable coatingcomposition comprises a monomer and/or oligomer of a (meth)acrylatecompound.
 26. The process of claim 16, wherein the curable coatingcomposition is cured through UV irradiation.
 27. The process of claim16, wherein the microstructure is a hologram or a microstructure havingantireflective properties.
 28. The process of claim 16, wherein themicrostructure is a periodically repetitive structure having a period of250 nm.
 29. The process of claim 16, wherein deposition step (j)comprises electrodepositing a metal or a metallic alloy.
 30. The processof claim 16, wherein the mold piece is nickel.
 31. The process of claim16, wherein the master article is an ophthalmic lens the main surface ofwhich is a spherical surface or a presbyopia correcting surface.